A sensor having a resin mold casing according to a prior art is shown in FIG. 2. The sensor is disclosed in U.S. Pat. No. 6,034,421. The sensor includes a molded IC 1 having an IC chip as a sensing element and a casing 2 having a connector portion. The molded IC 1 is primarily molded with thermosetting resin such as epoxy resin. The molded IC 1 is accommodated in the casing 2 by being secondarily molded with thermoplastic resin. In other words, the molded IC 1 is composed of thermosetting resin, and the casing 2 is made of thermoplastic resin.
Thus, the IC chip as a sensing element is primarily molded with thermosetting resin, and this molded IC chip, i.e., the molded IC 1 is secondarily molded with thermoplastic resin. This construction is for preventing a wire and the like in the sensing element from breaking of wire and for securing mechanical strength of the casing 2.
In this sensor, since the molded IC 1 is composed of thermosetting resin and the casing 2 is made of thermoplastic resin, adhesiveness between the molded IC 1 and the casing 2 is low. In some cases, a clearance may be formed between the molded IC 1 and the casing 2. Therefore, in general, the casing 2 covers entirely the molded IC 1 so that the casing 2 prevents moisture from penetrating into the sensor.
However, since the sensing element, i.e., the IC chip is entirely covered with thermosetting resin as a primary resin mold and thermoplastic resin as a secondary resin mold, the sensing element is separated from the outside environment as a measurement object. In other words, a distance between the sensing element and the outside environment becomes large. Therefore, it is difficult to increase the response of the sensor and/or the sensitivity of the sensor, so that the degree of freedom in design and specification of the sensor becomes lower. Moreover, a potting material as a sealing is necessitated for sealing between the molded IC 1 and the casing 2, so that a manufacturing cost of the sensor is increased.